BEIJING, Oct. 3 (Xinhua) -- China's railway freight volume, a key indicator of economic activity, slumped further in the first eight months of 2015, the country's top economic planner said on its website.

The railways transported 2.26 billion tonnes of cargo from January to August, down 10.9 percent year on year, compared with a decrease of 10.1 percent in the first half of the year, and a 9.4-percent drop in the first quarter, according to the National Development and Reform Commission.

In August alone, railways transported 280 million tonnes of cargo, down 15.3 percent year on year.

The sluggish figure came as another key index for manufacturing activity in August fell to the lowest level since August 2012.

China's manufacturing purchasing managers' index (PMI) for August came in at 49.7, according to data released by the National Bureau of Statistics (NBS) and the China Federation of Logistics and Purchasing.

A reading above 50 indicates expansion, while a reading below that represents contraction.

September's PMI slightly rebounded to 49.8, a reversal from two months of decline previously, but still fell into contraction territory for the fourth consecutive time this year, indicating anaemic demand and downward pressure in the manufacturing industry, earlier data showed.

Manufacturing is a key driver of China's growth. The country's GDP expanded 7 percent year on year in the first half, in line with the official growth target but still the lowest reading since the second quarter of 2009.